33“Again, you have heard that it was said to those of ancient times, ‘You shall not swear falsely, but carry out the vows you have made to the Lord.’ 34But I say to you, Do not swear at all, either by heaven, for it is the throne of God, 35or by the earth, for it is his footstool, or by Jerusalem, for it is the city of the great King. 36And do not swear by your head, for you cannot make one hair white or black. 37Let your word be ‘Yes, Yes’ or ‘No, No’; anything more than this comes from the evil one. (Matthew 5:33-37, NRSV)
Do not swear on anything but simply say yes or no.
Or to put it in a way that makes simple sense to everyone, “Say what you mean and mean what you say.”
There is truth in a liar has to have a good memory…